1. Field of the Invention
The present invention relates to a Braun Tube for projectors. Specifically, the present invention relates to a Braun Tube for projectors, in which an extended life cycle is achieved by constraining the degradation of the illuminant, constraining the browning phenomenon, as well as improving the spot size of the electron beam thereof.
2. Description of the Related Art
In recent years, an enlargement of the size of household television receivers has brought about a demand for sizes up to 50 inches or more. Nowadays, plasma display panels (PDP) have drawn attention as large-sized TVs. However, their high price has inhibited their acquisition by ordinary people, and, in addition, projectors utilizing liquid crystal that projects images on a screen (a front-type liquid crystal projector), projectors utilizing liquid crystal that project an image upon reflecting the image on a screen through a mirror positioned inside the TV set (a rear-type liquid crystal projector) and the like have been drawing attention. Nevertheless, these types of projectors are also expensive.
Front-type as well as rear-type projectors that utilize Braun tubes are inexpensive. Especially, the demand for the rear-type Braun tube projector for consumers has increased because they are less expensive than liquid crystal projectors and in view of the fact that they are able to achieve images of high definition; thus, the demand in the Asian and American markets has increased drastically.
Braun tube projectors have a Braun tube incorporated in the set. Projectors of 7 to 9 inches having a glass screen (phosphor screen) coated with monochromatic red, green and blue illuminants. Nowadays, the 7-inch type is dominant.
Also, in view of the fact that images are projected, it is desirable that the brightness generated from the Braun tube for projectors is as high as possible. In order to increase the brightness, it is necessary to increase the density of electric current to be applied to the Braun tube for projectors to approximately 10 times the direct viewing Braun tube (ordinary, conventional television receivers).
However, the higher the current density applied to the Braun tube for projectors, the more the illuminant deteriorates and the life cycle of the product is reduced. Concomitantly, the spot size of the electron beam originated from the electron gun is increased, thus incurring a problem of degrading the image quality. In addition, conventional Braun tubes for projectors have a great amount of clearances on the illuminant layer formed on the glass screen (phosphor screen), so that the glass screen is directly irradiated by electron beams, thus giving rise to the browning effect in which the glass screen turns out to be pigmented, and constituting another problem that affects the life cycle of the product.